<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>盒子模型</title>
    <style>
        #outer {
            height: 100px;
            width: 100px;
            padding: 10px;
            border: 1px solid hotpink;
            box-sizing: border-box;
        }
    </style>
</head>

<body>
    <div id="outer">
        this is box
    </div>
</body>

</html>